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Molecular mechanism for the Shp-2 tyrosine phosphatase function in promoting growth factor stimulation of Erk
1Department of Biochemistry and Molecular Biology and Walther Oncology Center, Indiana University School of Medicine and Walther Cancer Institute, Indianapolis, Indiana 46202-5254, USA.
Abstract:
We have previously shown that activation of extracellular signal-regulated kinase (Erk) by epidermal growth factor (EGF) treatment was significantly decreased in mouse fibroblast cells expressing a mutant Shp-2 molecule lacking 65 amino acids in the SH2-N domain, Shp-2(Delta46-110). To address the molecular mechanism for the positive role of Shp-2 in mediating Erk induction, we evaluated the activation of signaling components upstream of Erk in Shp-2 mutant cells. EGF-stimulated Ras, Raf, and Mek activation was significantly attenuated in Shp-2 mutant cells, suggesting that Shp-2 acts to promote Ras activation or to suppress the down-regulation of activated Ras. Biochemical analyses indicate that upon EGF stimulation, Shp-2 is recruited into a multiprotein complex assembled on the Gab1 docking molecule and that Shp-2 seems to exert its biological function by specifically dephosphorylating an unidentified molecule of 90 kDa in the complex. The mutant Shp-2(Delta46-110) molecule failed to participate in the Gab1-organized complex for dephosphorylation of p90, correlating with a defective activation of the Ras-Raf-Mek-Erk cascade in EGF-treated Shp-2 mutant cells. Evidence is also presented that Shp-2 does not appear to modulate the signal relay from EGF receptor to Ras through the Shc, Grb2, and Sos proteins. These results begin to elucidate the mechanism of Shp-2 function downstream of a receptor tyrosine kinase to promote the activation of the Ras-Erk pathway, with potential therapeutic applications in cancer treatment.
Insights
The phosphatase Shp-2 promotes the Ras-Erk pathway activation by dephosphorylating a 90 kDa protein in a Gab1 complex. Mutant Shp-2 impairs this process, affecting cell signaling and potentially cancer development.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Extracellular signal-regulated kinase (Erk) pathway activation is crucial for cellular processes.
- Shp-2 phosphatase plays a role in mediating Erk activation.
- Previous studies showed decreased Erk activation in cells with mutant Shp-2.
Purpose of the Study:
- To elucidate the molecular mechanism of Shp-2's positive role in Erk induction.
- To investigate Shp-2's function in signaling components upstream of Erk.
- To understand Shp-2's interaction with Gab1 and dephosphorylation activity.
Main Methods:
- Analysis of signaling component activation (Ras, Raf, Mek) in Shp-2 mutant cells.
- Biochemical assays to identify Shp-2's protein complex interactions.
- Assessment of Shp-2's dephosphorylation activity on specific protein targets.
Main Results:
- EGF-stimulated Ras, Raf, and Mek activation were significantly reduced in Shp-2 mutant cells.
- Shp-2 was recruited to a Gab1 complex upon EGF stimulation and dephosphorylated a 90 kDa protein.
- Mutant Shp-2 failed to engage in the Gab1 complex and dephosphorylate p90, leading to defective Erk cascade activation.
Conclusions:
- Shp-2 promotes Ras-Erk pathway activation by dephosphorylating a 90 kDa molecule within a Gab1-organized complex.
- The SH2-N domain of Shp-2 is critical for its recruitment to Gab1 and subsequent signaling.
- Shp-2's function is downstream of receptor tyrosine kinases and upstream of Ras activation, offering therapeutic potential in cancer.